The invention relates to an optical demultiplexer which comprises an optical input fibre for transporting a plurality of light signals of different wavelengths, a wavelength-selective member, at least one output member for receiving a light signal in a given waveband, and a lens system which is arranged between the wavelength-selective member on one hand and the input fibre and the output member on the other hand, the arrangement being such that between the input fibre and the output member there exists a low-loss transmission path which is dependent on the wavelength of the light.
A demultiplexer of this kind is known from "Applied Optics", Vol. 18, No. 16, Aug. 15, 1979, pages 2834-2836. The demultiplexer shown therein selects four colour bands (wavebands) from the available colour spectrum, each of said bands being situated around a fixed "central colour" or "central wavelength". In contemporary telecommunication networks, the colour bands in which information is transmitted in the form of light pulses of different colour have not yet been standardized. Therefore, it may be that colour bands will be standardized which do not correspond to the fixed colour bands, so that the demultiplexer can no longer be used in communication networks thus standardized.